1. Field of the Invention
The present invention relates to a wiper unit of a sewing machine for wiping a thread end of a needle.
2. Description of the Prior Art
Wiper units are used with sewing machines provided with thread cutting units. The cutting unit cuts off a needle thread and a bobbin thread under a processed cloth after completion of a stitching operation of a piece of processed cloth. The wiper unit wipes the thread end of the needle thread and thereafter draws the thread end over the processed cloth and the cloth presser to thereby prevent the first stitching portion of the needle thread from being loosened on the processed cloth and causing quality deterioration.
There are two types of prior art wiper units. In the first type the thread end is wiped at a forward movement wherein the wiper moves from a return state at the lower position to a lifting state. (The first type is hereafter referred to as the forward movement wiping system.) In the second type, the thread end is wiped at a backward movement wherein the wiper moves from a return state at the upper position to the lower position, and turns to the lifting position. (The second type is hereafter referred to as the backward movement wiping system.) Depending on conditions and specifications of the stitching of the processed cloth, the forward movement wiping system or the backward movement wiping system is selected by an operator for integral use with the sewing machine.
In the forward movement wiping system, since the wiper is adjacent to the processed cloth at the normal state of the sewing machine in the lower position, the wiper depending on the shape, the kind, and the like of the processed cloth can obstruct the stitching operation. In such case, the backward movement wiping system is adopted since it does not create an obstruction because the wiping unit is positioned in the return state at the lifting position.
Since the wiping operation is effected at the backward movement while the needle thread end is retracted by a hooked portion of the wiper in the backward movement wiping system, erroneous wiping operation is liable to occur when the forward movement of the wiper unit ensues before the needle thread is properly positioned.